Reevaluating the Solution Photophysics of Tetraphenylethylene at the Origin of their Aggregation-Induced Emission Properties.

Although tetraphenylethylene (TPE) and its derivatives have been the most commonly used building blocks in the con-struction of molecules with Aggregation-Induced Emission (AIE) properties, no absolute consensus exists regarding the mechanisms at the origin of the phenomenon. Restriction of Intramolecular Rotations (RIR) of peripheral phenyls has historically been a dominant paradigm which has served as a valuable guideline in the molecular engineering of AIEgens. Yet, an increasing number of recent works have established that photoisomerization or photocyclization may actively participate in the nonradiative dissipation of the excitation energy. In this paper, we bring the first experimental evalua-tion of the quantum efficiencies of these different processes, and show that photoisomerization is by far the dominant photophysical pathway in solution, accounting for virtually all nonradiative decay of the molecule's excited state in de-gassed solution.